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MECHANICAL ENGINEERING CRAFT OBJ (TYPE A)
01-10: ACCBCDAABC
11-20: CDACBDADBC
21-30: BACCBCABAA
31-40: DADB#BDADB
COMPLETED
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MECHANICAL ENGINEERING CRAFT ANSWERS (TYPE A)
ANSWER FIVE(5) QUESTIONS ONLY
(1a)
[TABULATE]
=PLANO MILLING MACHINE=
(i) Designed for machining large, heavy, and long workpieces such as machine beds and heavy steel plates.
(ii) The workpiece is mounted on a stationary table, and the milling heads move on a gantry/frame.
(iii) Capable of multiple milling heads operating simultaneously.
(iv) Used for heavy-duty, high-precision surface machining.
=ORDINARY MILLING MACHINE=
(i) Designed for machining smaller to medium-sized workpieces.
(ii) The table moves (longitudinal, cross, vertical) while the cutter is usually fixed on the spindle.
(iii) Usually has one milling head (horizontal/vertical).
(iv) Used for general milling operations such as slotting, keyway cutting, drilling, shaping.
(1b)
(i) To cool the cutting tool and workpiece by carrying away heat generated during machining.
(ii) To lubricate the cutting zone, reducing friction between the tool and the workpiece.
(iii) To flush away chips from the cutting area to prevent chip clogging.
(iv) To improve cutting performance by reducing tool wear and extending tool life.
(1c)
(i) High cooling ability to absorb and dissipate heat effectively.
(ii) Good lubricating property to minimize friction at the tool–workpiece interface.
(iii) Non-corrosive – should not rust or stain the machine, tool, or workpiece.
(iv) Low viscosity to ensure easy flow and penetration into the cutting zone.
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(2ai)
Shank : The shank is the cylindrical portion of the drill that is held by the drill chuck or machine spindle. Its purpose is to securely hold the drill in the machine and transmit the rotational motion from the spindle to the cutting edges.
(2aii)
Flute: The flute is the helical groove(s) along the drill body. Its purposes are:
-To provide cutting edges for material removal.
-To allow chips to escape from the hole being drilled.
-To permit cooling fluid to reach the cutting edges.
(2aiii)
Taper on the drill body: The taper is the conical portion at the rear of the drill. Its purpose is to fit into the machine spindle or socket, allowing easy installation and removal while ensuring secure and concentric alignment of the drill.
(2b)
(i) Always wear protective gear such as safety goggles and gloves to prevent injury from flying chips.
(ii) Ensure the workpiece is properly clamped to avoid movement or spinning during drilling.
(2ci)
Correct cutting speed: It ensures efficient material removal, reduces tool wear, prevents overheating, and gives a good surface finish.
(2cii)
Correct feed rate: It ensures proper penetration of the drill, prevents tool breakage, avoids poor hole quality, and maintains dimensional accuracy of the hole.
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(4a)
WORKING PRINCIPLE:
A shaper is a machine used to produce flat surfaces, grooves, and slots by reciprocating linear motion of a single-point cutting tool over a stationary workpiece. The cutting occurs only in the forward stroke, while the return stroke does not cut but the tool moves back to start a new cut.
OPERATION:
(i) The workpiece is clamped on the table of the shaper.
(ii) The cutting tool is mounted on the ram, which moves back and forth.
(iii) During the forward stroke, the tool removes material, producing the desired shape or surface.
(iv) During the return stroke, the tool is lifted slight to avoid cutting.
(v) The table can be adjusted vertically and horizontally to allow multiple passes for achieving the required dimensions and finish.
(4b)
(i) Workpiece Movement: In a planer, the workpiece moves back and forth, while in a shaper, the tool (ram) moves back and forth and the workpiece remains stationary.
(ii)Size of Workpiece: A planer can machine large and heavy workpieces, whereas a shaper is typically used for smaller workpieces.
(iii) Cutting Stroke: Planers usually have longer strokes suitable for heavy cuts, while shapers have shorter strokes suitable for lighter cuts.
(iv) Number of Tools: Planers can use multiple tools simultaneously, whereas shapers usually use one tool at a time.
(v) Applications: Planers are used for machining large flat surfaces like machine beds, while shapers are used for smaller flat surfaces, grooves, and keyways.
(4c)
[DRAW THE DIAGRAM]
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(6a)
(i) Material to be ground: Different abrasive materials are suitable for different workpiece materials. Aluminium oxide is commonly used for steels because it withstands the toughness of steel, while silicon carbide is preferred for cast iron, non-ferrous metals, and non-metallic materials due to its sharpness and brittleness.
(ii) Grit size: Grit size determines the cutting action and surface finish. Coarse grit, which has larger abrasive grains, is used for rapid stock removal and rough grinding operations. Fine grit, with smaller grains, is used when a smooth finish and high surface quality are required.
(iii) Wheel hardness (Grade): The grade represents how firmly the abrasive grains are held in the wheel. Harder grades are suitable for soft materials and small contact areas because they offer longer wheel life. Softer grades are used for hard materials that quickly dull the abrasive grains and therefore require frequent shedding of worn grains for effective cutting.
(iv) Type of bond: The bond is the material that holds the abrasive grains together, and it affects wheel strength, heat resistance, and flexibility. Vitrified bonds are hard, rigid, and heat-resistant, making them suitable for general grinding. Resinoid or rubber bonds are more elastic, providing flexibility for rough cutting, high-speed grinding, or certain finishing operations
(6b)
N = (V × 1000)/(π × D)
Given:
-Cutting speed, V = 48 m/min
-Drill diameter, D = 14 mm
-π = 3.142
Substituting in the values:
N = (48 ×1000)/(3.142 ×14)
N = 4800/43.988
N = 1091.2 rev/min
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(7a)
(i) Type of cut refers to the pattern or arrangement of the teeth on a file, while grade of cut refers to the coarseness or fineness of the teeth.
(ii) Type of cut describes whether the file has single-cut, double-cut, rasp-cut or curved-cut teeth, whereas grade of cut describes bastard, second-cut, or smooth type based on teeth spacing.
(iii) Type of cut determines the direction and shape in which the teeth remove metal, while grade of cut determines how much material is removed per stroke.
(7bi)
(i) Removes Oxides from Metal Surfaces: Flux helps to clean and dissolve oxide layers that form on the metal when heated, ensuring a clean surface for solder flow.
(ii) Prevents Further Oxidation During Heating: When the metal is heated, it quickly reacts with oxygen to form new oxides. Flux shields the metal surface and prevents more oxidation.
(iii) Improves Wetting and Flow of Solder: Flux helps solder spread evenly by reducing surface tension, allowing it to flow smoothly into joints and gaps.
(iv) Enhances Strong and Reliable Joints: By cleaning the surface and improving solder flow, flux ensures strong metallurgical bonding between the metals.
(7bii)
[DRAW THE DIAGRAM]
(7c)
[DRAW THE DIAGRAM]
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